Applied in automation technology, especially in process automation technology, are field devices, which serve for determining and monitoring process variables. Examples of such field devices are fill level measuring devices, flow measuring devices, analytical measuring devices, pressure- and temperature measuring devices, moisture- and conductivity measuring devices, density and viscosity measuring devices. The sensors of these field devices register the corresponding process variables, e.g. fill level, flow, pH-value, substance concentration, pressure, temperature, moisture, conductivity, density and viscosity. A large number of such field devices are produced and sold by members of the firm, Endress+Hauser.
Produced and sold by the applicant under the marks, LIQUIPHANT, LIQUIPOINT and SOLIPHANT, are sensors for detecting a predetermined fill level. They are preferably applied as running dry protection for pumps or as overfilling preventers and have usually two antivalent switch outputs, via which the particular switch state of the field device is output. These sensors, which are also referred to as limit level switches, have for reasons of leak proofing and/or space saving often no integrated optical displays (LED) for the two antivalent switch outputs. Especially is this the situation in the case of encapsulated field devices, which satisfy the IP69K standard. Since the on-site information concerning the respective switch output, respectively switch state of the limit level switch, is usually, however, very important for a customer, LEDs, which visualize the switch outputs, are integrated in the connection plug of the plug connector connected with the sensor. Used as connection plug in automation technology are often M12 plugs. The connection plugs offered in the market for field devices are, indeed, able, via LEDs, to visualize the two antivalent switch outputs and the operating voltage; however, they are not able, supplementally, to indicate disturbances or malfunctions of the field device on-site (thus at the site of integration into the process). Thus, extremely important on-site information is missing for customers operating a plant, in which the field device is installed. The disadvantage in the case of the known embodiment of the connection plug is especially that a defective or malfunctioning working field device can only be replaced with a more or less large time delay, since a technician cannot detect the disturbance or malfunction directly on-site. The ability of the plant to function can, consequently, in given cases, be significantly degraded due to malfunction of a field device.